The present invention is generally directed to control devices for gas-fired water heaters and more particularly pertains to gas flow control valves as well as safety mechanisms that guard against the build-up of excess heat and/or pressure within water heaters.
Gas fired water heaters typically rely on a gas valve that controls the flow of gas to the burner in order to maintain the temperature of the water contained in the tank within preselected limits. As the water temperature drops below a preselected lower limit, the valve opens to permit the flow of gas to the burner where it is ignited by a pilot flame or electronic means. When the temperature of the water exceeds a preselected upper limit, the valve shuts off the flow of gas. Such temperature regulation is typically achieved with the use of a temperature sensor that must be immersed in the water within the tank and therefore requires the wall of the tank to be penetrated. In common use is an Invar rod type sensor which extends through the tank wall into the water contained therein, wherein the distal end of an Invar rod is affixed to the distal end of a concentrically positioned copper sleeve. The disparate rates of thermal expansion of the two materials causes the proximal ends of the rod and sleeve to undergo relative movement which is advantageously employed to open and close the gas valve.
Water heaters are usually additionally fitted with a pressure relief (PRV) valve that serves to vent water from within the tank should it exceed a preselected pressure. Such safety device prevents a build up of excessive pressures that could cause catastrophic failure of the tank. When the water pressure exceeds the preselected limit, the PRV valve opens to relieve excessive pressure to a vent line that conducts the released water to a safe location. The fitting of a PRV valve inherently requires another penetration of the tank wall.
Water heaters are typically also protected against the build up of excessive temperatures with the use of a relief valve that is actuated by a temperature sensor. The sensors in common use must be immersed in the water and therefore another penetration of the tank wall is required. Such device may be combined with the pressure relieve valve wherein a single valve mechanism is actuatable by either the temperature sensor or directly by water pressure thereby achieving both functions with a single perforation of the water tank.
Another device fitted to most water heaters is a drain valve that allows the water to be drained from the tank. This is necessary to enable the tank to be moved or to be flushed. The valve is typically located near the bottom of the tank in an easily accessible location.
A disadvantage of the prior art approach to the use of these various control and safety devices is inherent in the fact that each requires a separate hole to be formed in the water heater tank, the welding of a threaded fitting thereto and the threading of the respective device thereinto. Not only is such manufacturing process relatively labor intensive, but the mounting of each of such device then poses a potential for leakage throughout the service life of the water heater. Additionally, each device that protrudes from the tank not only serves as a conduit for heat loss but may also serve to disrupt the continuity of insulation that is fitted about the tank to further compromise the ability of the water heater to retain heat. Finally, the protrusion of these various devices through the outer skin of a water heater is unsightly which may be problematic for installations wherein the water heater is positioned in plain sight.
It would therefore be advantageous to reduce the number of devices that must be attached to a water heater in order to properly and safely control its operation. Such improvement would expedite the assembly process, reduce the potential for leaks and reduce heat loss to improve the overall efficiency of the water heater.
The present invention overcomes the disadvantages associated with prior art control and safety devices utilized on water heaters. The control device of the present invention may integrate any combination of the gas flow control valve actuator, pressure relief valve, temperature relief valve and drain cock in a single housing that requires only a single fitting to be attached to the tank. This greatly reduces the potential for leakage, reduces manufacturing costs, reduces heat loss to improve the overall efficiency of the water heater and provides for a smoother, less cluttered outward appearance.
A preferred embodiment of the control device of the present invention employs an Invar rod mechanism to sense water temperature and actuate the gas valve. The interior of the housing through which the Invar rod extends from the gas valve into the interior of the tank is in fluid communication with the tank. A port is formed in such housing which is sealed off by a relief valve that is biased against a valve seat by a spring. The spring is oriented and configured such that in the event the water pressure within the tank and hence within the housing rises to a level that overcomes the biasing action of the spring, the relief valve opens to release water through the port. The force of the spring may also be overcome by manual means so as to enable the same relief valve to be used as a drain cock. A temperature sensor also manipulates the relief valve. A temperature in excess of a preselected amount causes the spring tension to be overcome and the valve to open. The same valve is therefore used to manually drain the tank as well as to automatically reduce excessive water temperature or pressure.
These and other features and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment which, taken in conjunction with the accompanying drawings, illustrates by way of example the principles of the invention.